Postoperative pain after total knee arthroplasty (TKA) can be difficult to manage and may delay recovery. There are multimodal postoperative pain management after TKA, including intravenous opioids, epidural analgesia, peripheral nerve blocks or periarticular infiltration with local anesthetics. All of these treatments may lead to side effects such as nausea, headache, hypotension, urinary retention, partial motor block and infection of the knee. Therefore the investigators will compare three methods of postoperative analgesic after TKA by their efficiency and complication.

This group uses local analgesia infusion pump of 0.2% ropivacaine 360ml through periarticular infiltration for postoperative analgesia.

Procedure: Local analgesic

Patient will be performed under combined lumbar plexus and sciatic nerve block with 0.33% ropivacaine.At the end of surgery,two catheters are left in the wound.One is intraarticular and the other is on the surface of articular cavity.And then a pump elastomeric infusion pump will be connected with the catheters, which runs 5mL every hours.

Drug: ropivacaine

0.2% ropivacaine

Active Comparator: Nerve Block

People in this group will receive a postoperative pain management by continuous lumbar plexus block with 0.2% ropivacaine.

Procedure: Nerve Block

Combined lumbar plexus and sciatic nerve block with 0.33% ropivacaine will be performed before the surgery.After the a bolus of 30mL ropivacaine around lumbar plexus,a catheter will be left in Psoas gap with 6cm.A pump elastomeric infusion pump running 5mL every hours will also be connected with the catheters at the end of the operation.

People in this group will also receive an anesthesia of combined lumbar plexus and sciatic nerve block with 0.33% ropivacaine.An intravenous electronic analgesia pump infusion of flurbiprofen axetil 250mg,palonosetron 0.5mg,pentazocine 240mg.dezocine 30mg will will provide postoperative pain management.The patients will received a 2 mL/h continuous basal infusion and 1 mL boluses with a lockout time of 30 min after a 5 mL Loading dose at the end of the surgery.

People who were postoperative consciousness, language or hearing impaired

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Please refer to this study by its ClinicalTrials.gov identifier: NCT02094339